1. Field of the Invention
The present invention relates to a Lewis acid catalyst composition which can be applied to various acid catalytic reactions. More particularly, the present invention is concerned with a Lewis acid catalyst composition comprising a specific mixed medium and a Lewis acid catalyst which is at least one compound selected from the group consisting of specific organic compounds containing a rare earth element. By the use of the Lewis acid catalyst composition of the present invention for an acid catalytic reaction, after the reaction, not only can the Lewis acid catalyst be easily separated and recovered from the catalytic reaction mixture containing the same, but also the recycling of the Lewis acid catalyst can be performed without suffering a lowering of the catalytic activity. The present invention is also concerned with a novel Lewis acid catalyst.
2. Prior Art
A Lewis acid catalyst has been employed in various acid catalytic reactions for the synthesis of organic compounds. However, the use of the Lewis acid catalyst in the catalytic reaction system has a problem in the commercial practice of the catalytic reaction because, after the reaction, the separation and recovery of the catalyst from the reaction system and the recycling of the recovered catalyst are accompanied with difficulties. For solving such a problem, a number of proposals have been made with respect to methods for separating and recovering a Lewis acid catalyst employed in a reaction. As an example of the methods, there can be mentioned a method in which a Lewis acid catalyst is fixed. For example, a study has been made about the method which comprises fixing a catalyst to an inorganic or a macromolecular carrier to thereby obtain a fixed catalyst, effecting a solid phase synthesis reaction by using the obtained fixed catalyst, and then recovering the fixed catalyst from the synthesis reaction system. However, the solid phase synthesis reaction has problems in that not only is the catalytic activity lowered, but also the solid phase synthesis reaction is not applicable to all of the organic syntheses which are generally conducted in a liquid phase.
Therefore, it has been desired to develop a technique which is advantageous not only in that a reaction efficiency in a liquid phase is increased, and a post-treatment of the reaction mixture can be done simply, but also in that the catalyst used can be easily recovered and recycled. Recently, a reaction method is disclosed in U.S. Pat. No. 5,463,082 in which a reaction solvent comprising a fluorocarbon, such as perfluoromethylcyclohexane, and a non-fluorinated hydrocarbon, such as toluene, and a catalyst, such as a group VIII metal complex containing perfluoroalkyl chains or fluorinated alkyl chains, are used. In the reaction system of this method, a reaction product and the catalyst are separately dissolved in the non-fluorinated hydrocarbon phase and the fluorocarbon phase, respectively, so that the recycling of the catalyst becomes possible. However, in the method of this prior art, it is required to use the catalyst which can be dissolved in the fluorocarbon. Therefore, the number of the catalysts which can be used in the method of the prior art is limited. Further, the reactions exemplified in this prior art are limited to oxidation by molecular oxygen and hydroformylation.
Unexamined Japanese Patent Application Laid-Open Specification No. 11-246564 discloses that a rare earth complex of a bis(perfluoroalkylsulfonyl)imide can be dissolved in a partly fluorinated hydrocarbon in the presence of a nucleophilic compound. However, this document does not disclose the recovery of the dissolved catalyst by phase separation of the solvent and the recycling of the catalyst.
Therefore, it has been desired to develop an improved reaction system which is advantageous in that a reaction efficiency in a liquid phase is increased, and not only can a reaction product be recovered easily, but also the catalyst used can be easily recovered and recycled.
In this situation, with a view toward solving the above-mentioned problems, the present inventors have conducted extensive and intensive studies about the mutual behaviors of raw materials, a Lewis acid catalyst, a reaction medium and a reaction product in a reaction system containing these substances. As a result, it has unexpectedly been found that, when a specific Lewis acid catalyst composition (containing as a Lewis acid catalyst a highly active rare earth salt of a perfluoroalkylsulfonyl compound) is used in combination with a raw material or raw materials for the intended reaction to thereby form a reaction system, not only can the catalyst exhibit high catalytic activity in a liquid phase reaction, but also the resultant reaction mixture can separate into a phase having the catalyst dissolved therein and a phase having a reaction product dissolved therein. The above-mentioned specific Lewis acid catalyst composition, in one aspect, comprises the Lewis acid catalyst and a mixed medium comprising a perfluorinated aliphatic hydrocarbon or alicyclic hydrocarbon and at least one non-fluorinated hydrocarbon selected from the group consisting of a hydrocarbon and a halogenated hydrocarbon, exclusive of a fluorinated hydrocarbon, wherein the at least one non-fluorinated hydrocarbon is generally known as a solvent capable of dissolving therein not only a raw material or raw materials conventionally used for an acid catalytic reaction but also a reaction product. In another aspect, the Lewis acid catalyst composition comprises the Lewis acid catalyst and a mixed medium comprising a perfluorinated aliphatic hydrocarbon or alicyclic hydrocarbon, a perfluorinated aromatic hydrocarbon and water. The present invention has been completed, based on the above novel finding.
On the other hand, in the course of the above-mentioned study, the present inventors have also found a novel rare earth salt of a perfluoroalkylsulfonyl compound which is stable to water and has high catalytic activity as compared to the conventional Lewis acid catalysts.
Accordingly, it is an object of the present invention to provide a Lewis acid catalyst composition which, when used for effecting a reaction in the presence of a raw material or raw materials, enables a catalyst and a reaction product to be easily separated and recovered from the resultant reaction mixture, so that the recycling of the catalyst becomes possible.
It is another object of the present invention to provide a Lewis acid catalyst composition capable of achieving a high reaction efficiency in a reaction in a liquid phase having a Lewis acid catalyst contained therein.
It is still another object of the present invention to provide a Lewis acid catalyst composition in which water is additionally added to a mixed medium.
It is a further object of the present invention to provide a novel Lewis acid catalyst which is stable to water and has high catalytic activity as compared to the conventional Lewis acid catalysts, and which can be widely used for various acid catalytic reactions.
The foregoing and other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description and the appended claims taken in connection with the accompanying drawings.